Power module

ABSTRACT

A power module is suggested having a simple and cost-effective arrangement and ensuring a reliable operation. To this end, a circuit arrangement comprising at least one electronic component is arranged on a carrier body. A conductor pattern is formed on the top side of the carrier body, and a structured cooling element made of the material of the carrier body, is provided on the bottom side. The invention also relates to a power module as power converter for electric motors.

[0001] Electronic modules are used in many areas for different objectives and applications. Electronic modules constructed as power modules are used particularly for control purposes, for example for the closed loop control of the r.p.m. and of the power of electric motors.

[0002] Electronic components for providing the required power are part of such power modules. For example, in connection with electric motors the power is typically in the kilowatt range. Power modules are used for providing control signals and/or for the evaluation of measured signals. As a rule, the active and passive components of the circuit arrangement of such power module require a construction that has a low inductance to avoid excess voltages. Active components include, for example, power components that are working in a switching operation at high speed current changes, particularly integrated switching circuits operating as power switches. Passive components include, for example resistors, for example shunts for current measuring, and capacitors. Thus, the circuit arrangement of the power module is customarily applied on an insulating carrier body or an insulating substrate consisting as a rule of a ceramic material. For mechanical stabilization and for heat dissipation of the dissipation power of the components of the circuit arrangement, particularly the power components, the carrier body is secured to a massive metallic cooling body, for example a copper or an aluminum plate. The carrier body is secured to the cooling body by a bonding layer, for example by means of solder or a heat conducting paste to form a thermal connection. The insulation or potential separation between the electronic components of the circuit arrangement and the cooling body is realized through the insulating carrier body.

[0003] The substrate or the carrier body and the cooling body have different thermal expansion coefficients since the former is made of ceramic material and the latter is made of metal. Therefore, the substrate and the cooling body have different thermal expansions. As a result, on the one hand, a relatively thick bonding layer is required between the carrier body and the cooling body, particularly in connection with a carrier body having a large surface for equalizing tensions. The thick bonding layer causes a high heat resistance particularly due to inclusions in the bonding layer such as shrink holes in a solder layer, which negatively influence the heat conductivity. Thus, a poor heat transition exists between the electronic components of the circuit arrangement and the cooling body due to the heat resistances that are formed by the inclusions. As a result, the dissipation of the dissipation power of the electronic components becomes difficult. On the other hand, the connection between the carrier body and the cooling body is frequently impaired, whereby the life duration and thus the reliability of the power modules is significantly reduced. This is particularly true where the power module must work in a large temperature range and under the temperature changes that such a large range entails.

[0004] It is the object of the invention to provide a power module that has a simple construction, a simple production at low cost while achieving a high reliability and advantageous thermal characteristics.

[0005] This object has been achieved according to the invention by the features of Patent claim 1.

[0006] Advantageous embodiments of the invention are part of the remaining patent claims.

[0007] The following components are particularly provided as parts of the power module.

[0008] A thick carrier body is made of an insulating material which has a high heat conductivity, which, for example, is made as a ceramic carrier of a ceramic material such as aluminum oxide Al₂O₃ or aluminum nitride AlN. The carrier body can be produced by drop forging tools, for example by dry presses or by means of injection casting followed by sintering. The thickness of the carrier body is selected with regard to the following measures, its size, particularly it surface, and the mechanical loads that are caused by the installation of the power module at its point of use, for example by a screw connection and which loads are further caused by the cooling, for example by the pressure of a coolant in a cooling circuit to which the power module is connected. A structured partial section of the ceramic carrier body functions simultaneously as a cooling element in that geometric elements are provided at the bottom of the carrier body which geometric elements are made of the material of the carrier body. These geometric elements are provided in an array in a determined arrangement and with a determined geometric form, for example in the shape of a peg or rhombus.

[0009] A metallic conductor structure is applied to the top surface of the carrier body. The conductor structure includes conductor tracks, mounting positions, contact pads, and terminal positions directly applied to the surface of the ceramic carrier body that is without any intermediate layers, for example by active soldering (active metal bonding) in that the conductor structure is chemically soldered directly to the surface of the carrier body by an oxide bonding or by a DCB-method. The DCB-method involves mechanically anchoring the conductor structure in the carrier body through the molten metal of the conductor structure, particularly in the pores of the ceramic carrier body. The electronic components of the circuit arrangements can be interconnected through the conductor structure with one another and/or with connector contacts in an electrically conducting manner.

[0010] The electronic components of the circuit arrangement are mounted to the mounting positions of the conductor structure, particularly the power components, for example in the form of silicon chips. The mounting may for example be accomplished with soft solder or by pressing. The silicon chips are contacted with each other and/or with the conductor structure, for example by means of wire bonds by contacting the terminals of the electronic components through bond wires with certain contact pads of the conductor structure or with terminals of further components. The connection may also be done by a low temperature sintering method by a direct application of the terminals of the electronic components to one another and sintering. Furthermore, connector contacts are secured to the terminal positions of the conductor structure for the external connection of the power module to further structural groups or components.

[0011] The heat dissipation of the circuit arrangement (of the dissipation power of the electronic components of the circuit arrangement) takes place through the structured cooling element formed on the underside of the carrier body away from the carrier body. The contour of the cooling element that is constructed as an array with a multitude of similarly structured geometric elements is adapted to the shape of the carrier body. The size or surface of the array depends on the dissipation power that must be dissipated. Stated differently, the required cooling function must be assured by the geometric elements of the array. Accordingly, a certain number of geometric elements is arranged equidistant one behind the other for forming a row. The geometric elements of two neighboring rows are respectively staggered relative to one another, preferably in such a way that the geometric elements of one row are positioned in the gap that is defined by the spacing of the geometric elements of the neighboring row. The shape, number and arrangement of the geometric elements, particularly the arrangement of the geometric elements relative to one another and the arrangement of the geometric elements in the array is adapted to the respective purpose of use of the power module and to the required cooling power. The geometric elements are, for example, shaped as rhombuses, frustums, pegs, or lentils and have, for example, a slightly slanted side surface. The cooling element is produced in the same production step and in the same tool as the carrier body, for example, in drop forging tools, for example by means of dry presses or by means of injection molding followed by sintering. That means, the geometric elements that are made of the same material as the carrier body and are removed together with the carrier body from a mold having a respective mold pattern. The cooling element or the array of the geometric elements is particularly integrated into a cooling circuit. For example, a coolant such as water or air of the cooling circuit flows through the array. The flow channels for the coolant of the cooling circuit are determined by the geometric elements of the array in that the coolant flows between the geometric elements, or rather between the various rows of geometric elements. The heat transition from the carrier body through the cooling element to the coolant can be adjusted or adapted. By predetermining the arrangement and the structure or shape of the array and thus of the geometric elements.

[0012] The power module combines within itself several advantages. The carrier body serves for the heat dissipation as well as a circuit carrier or substrate for the electronic components of the circuit arrangement. The carrier body also serves as a seal when the power module is directly arranged in a cooling circuit and thus it serves for the integration of the array of the geometric elements into the cooling circuit. By the direct connection of the electronic components of the circuit arrangement on the carrier body and by the direct connection of the cooling elements to the carrier body without any intermediate layers a small thermal resistance is obtained, whereby thermal problems can be avoided so that a high reliability and useful life of the power module are achieved. By preselecting the structure of the cooling elements a sufficient heat dissipation of the electronic components of the circuit arrangement is assured, particularly a variably selectable heat dissipation can be achieved by a respective shaping of the cooling element and thus of the geometric elements so that particularly in connection with an integration of the cooling element into the cooling circuit of a cooling system the through-flow velocity of the coolant and the pressure loss in the cooling circuit can be adapted to the requirements. The production effort and expense is small because a simple production of the cooling element is possible, particularly in combination with the carrier body in a single production step in the same tool. Thereby, manufacturing problems can be avoided which entails small manufacturing costs, particularly also due to the use of simple and low cost materials.

[0013] The power module will be explained with reference to an example embodiment in connection with the drawings (FIGS. 1 to 3). The Figures show:

[0014]FIG. 1 a view of the top side of the power module,

[0015]FIG. 2 a sectional view of the power module, and

[0016]FIG. 3 a bottom view of the power module.

[0017] The power module 1 is for example used as a power converter for liquid cooled electric motors in the field of motor vehicles (power for example 10 kW). Due to the occurring high dissipation power the power converter 1 is coupled directly to the liquid cooling at the electric motor, i.e. it is integrated into the cooling circuit of the electrical motor which cooling circuit is operated with the coolant water.

[0018] The power converter 1 comprises the following components:

[0019] A carrier body 2 as a circuit carrier formed, for example as a ceramic substrate or ceramic carrier made of, for example aluminum nitride (AlN) and having, for example the dimensions of 90 mm×57 mm×3 mm. The carrier body 2 is directly integrated into the cooling circuit and thus takes over the sealing of the cooling circuit relative to the further components of the power converter 1.

[0020] A conductor structure 7 having a thickness of, for example 0.3 mm is applied to the top side 14 of the carrier body 2. The conductor structure 7 is made, for example of copper and includes conductor tracks 8, mounting positions 13, contact pads 9 and terminal positions 11. The conductor structure 7 is applied, for example by means of a direct or active soldering process to the carrier body 2 by chemical soldering. The electronic components 5 of the circuit arrangement 6 are contacted at the contact pads 9, i.e. connected in an electrically conducting manner with the conductor structure 7. Connector contacts 12 are secured to the terminal positions 11, for example soldered by means of solder 20.

[0021] A circuit arrangement 6 comprising electronic components 5 is arranged on the carrier body 2. The circuit arrangement 6 comprises particularly power components for realizing the converter function and the resulting control of the electric motor. The electronic components 5 of the circuit arrangement 6 are silicon chips which are secured to the mounting positions 13 of the conductor structure 7, for example by means of a soft soldering process. For example, the chips are connected through bond connections 10 with the contact positions 9 of the conductor tracks 8 of the conductor structure 7 and/or with other electronic components 5.

[0022] The dissipation power of the electronic components 5 of the circuit arrangement 6, particularly of the power components, is discharged through the carrier body 2 and the cooling element 3 to the cooling circuit through which the coolant water is flowing. For this purpose the cooling element 3 is arranged on the underside 15 of the carrier body 2. The cooling element 3 is produced together with the carrier body 2 in a drop forging tool by pressing and is made, for example of aluminum nitride (AlN). The cooling element 3 is structured in a certain manner for forming an array 21 of geometric elements 4, whereby the geometric elements 4 of the cooling element 3, for example have a shape similar to a rhombus. The side surfaces of the shape are slightly beveled. For forming flow channels 18 for the coolant, the geometric elements 4 of the cooling element 3 are arranged in a certain number in a row 17 equidistant one behind the other and in different neighboring rows 17 staggered relative to one another. Particularly, two neighboring rows 17 are so staggered that the geometric elements 4 of a row 17 are positioned in the gap that is defined by the spacing of the geometric elements 4 between the geometric elements 4 of the neighboring row 17. For example, twelve geometric elements 4 are arranged one behind the other in a row 17 along a length of, for example 80 mm. Six different rows 17, for example are arranged staggered to one another on a width of, for example 40 mm. The geometric elements 4 of the cooling element 3 project with a height of, for example 6 mm into the cooling circuit of the electric motor and the coolant water flows through the cooling elements in accordance with the flow channels 18 formed by the arrangement of the geometric elements 4, whereby a certain flow direction and a certain flow velocity of the cooling water is predetermined. 

1. Power module (1) with a carrier body (2) for mounting a circuit arrangement (6) with at least one electronic component (5), a conductor structure (7) formed on the top side (4, 14) of the carrier body (2) and a cooling element (3) formed on the underside (15) of the carrier body (2) and structured of the material of the carrier body (2).
 2. The power module of claim 1, characterized in that the cooling element (3) is formed of an array (21) with a multitude of geometric elements (4) having a predetermined layout.
 3. The power module of claim 1 or 2, characterized in that the geometric elements (4) are arranged in several rows (17) staggered to one another, and in that a plurality of geometric elements (4) are equidistantly arranged in a row (17).
 4. The power module of claim 2 or 3, characterized in that the geometric elements (4) are shaped approximately like a rhombus.
 5. The power module of one of claims 1 to 4, characterized in that the conductor structure (7) arranged on the top side (14) of the carrier body (2) comprises conductor tracks (8), mounting positions (13) for holding electronic components (5) of the circuit arrangement (6), contact pads (9) for contacting the electronic components (5) of the circuit arrangement (6) and terminal positions (11) for the connection of the connector contacts (12). 